Method for producing composite oxide of metal

ABSTRACT

A process for producing a complex oxide containing the valuable metal and an alkali (earth) metal salt, which comprising co-milling a mixture of the valuable metal oxide and/or a precursor thereof, or a mixture of a substance containing the valuable metal oxide and/or a precursor thereof, with an alkali (earth) metal salt to a particle size of the valuable metal oxide or a substance containing the oxide, of 10 μm or less, and heating the co-milled product to a temperature of at least 200° C. so as to induce a solid-phase reaction of the valuable metal oxide with an alkali (earth) metal salt. The process improves the solid-phase reaction rate and the selectivity of the value metal complex oxide, which results in the enhancement of the productivity for the complex oxide.

TECHNICAL FIELD

The present invention relates to a process for preparing a complex oxideof a metal with an alkali metal and/or alkaline earth metal by carryingout a solid-phase reaction between the oxide of a metal and/or aprecursor thereof, or a substance containing the metal oxide and/or asubstance containing the precursor thereof, with an alkali metal saltand/or an alkaline earth metal salt.

BACKGROUND ART

The content of metal oxides and/or their precursors present in base ore,refined ore, incinerator ash and the like is at most several percent bymass. For example, one known process for recovering vanadium oxide frombase ore containing such a small amount of vanadium oxide involvesroasting the vanadium oxide-containing ore for several hours togetherwith soda ash (sodium carbonate) in an oxidizing atmosphere at anelevated temperature of 900 to 1200° C. to form sodium vanadate,extracting the sodium vanadate with water to obtain an aqueous solutionof sodium vanadate, then additionally refining to ultimately yieldvanadium oxide (U.S. Pat. No. 3,320,024).

However, in this method of recovery, heating the several percent byweight or less of vanadium oxide within the ore for a long period oftime at an elevated temperature of about 1000° C. requires a largeamount of energy. Additional problems include the large scale of theequipment needed, high investment costs, and the strict specificationsfor high-temperature durability of the facility. Moreover, because thisprocess involves a high-temperature reaction with an alkali, the bricksmaking up the equipment undergo alkali corrosion, so that maintenance isdifficult (JP 2001-519751 A).

Likewise, in the preparation of a complex oxide by roasting chromium orecontaining several tens of percent by weight of chromium oxide togetherwith an alkali metal compound, because it is necessary to heat thealkali metal compound to 1000 to 1200° C., problems like those in thecase of vanadium oxide similarly exist (JP 48-38817 A).

A process has been proposed for reacting tungsten oxide-containingwolframite or scheelite with an alkali metal compound at 500 to 800° C.to obtain water-soluble tungsten valuables which are then extracted withwater. However, this process has a low yield, in addition to which it isnecessary to heat and re-react the extraction residue (JP 55-89446 A)

Mechanochemical treatment, which refers to reaction processes that donot involve heating, are also known. Such treatment is typically carriedout by applying mechanical energy to a solid substance such as byshearing, compression, impact, grinding, bending, stretching, theninfluencing the chemical state such as by bringing about chemicalchanges in gaseous and liquid substances located near the solidsubstance, or by directly inducing, or promoting, chemical changesbetween these gaseous and liquid substances and the surface of the solidsubstance. Various treatment methods of this type have been described.

For example, JP 11-71111 A describes a method for the extraction ofrare-earth metal-containing substances in which a rare earthmetal-containing substance is mechanochemically treated in a planetarymill, then leached with a low-concentration acid.

JP 2001-11549 A discloses an indium-containing compound leaching processwhich involves subjecting an indium-containing compound tomechanochemical treatment in the presence of a ceramic powder, thenleaching the compound with a low-concentration acid at ambienttemperature.

In addition, JP 11-310442 discloses a process in which calcium oxide ismixed with coal ash and mechanochemically treated, thereby producing ahydraulic treated product in powder form.

However, because mechanochemical treatment is based on the promotion ofreactions by point contact at active sites on solid substance surfacesrenewed by mechanical action such as impact, increasing the amount ofreaction that takes place (i.e., the amount of product) requires that ameans be employed for continuing such treatment over a long period oftime so as to repeatedly renew the surface. Hence, this approach isfundamentally unsuitable for production on an industrial scale.

DISCLOSURE OF THE INVENTION

I have found that, although mechanochemical treatment does contain majorproblems in terms of productivity, if such treatment is applied to areaction between an oxide of a value metal and an alkali or alkalineearth metal salt, then the product of such treatment is heated to aspecific temperature, the reaction will proceed at a higher thanexpected rate. That is, as a result of extensive investigations Iconducted on ways for employing the merits of mechanochemical treatmentto increase productivity, I have discovered that by heating an alkalimetal or alkaline earth metal salt which has been brought into contactand is present together with the solid surfaces of an oxide of such avalue metal that has been rendered into fine particles by mixing andgrinding to renew the surface, the alkali metal or alkaline earth metalsalt diffuses from the solid surface to the interior of the value metaloxide, vastly increasing opportunities for contact (i.e., opportunitiesfor reaction) between the value metal oxide and the alkali metal oralkaline earth metal salt even at the interior of the solid, thusincreasing the reaction rate and lowering the starting temperature ofthe reaction compared with prior-art methods. Hence, at the sametemperature, the amount of reaction that takes place is greater,resulting in a higher productivity than in the prior art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the thermal analysis results obtained for co-milledvanadium-containing magnetite in Example 1 according to the invention.

FIG. 2 shows the thermal analysis results obtained for milledferroniobium alloy in Example 2 according to the invention.

FIG. 3 shows the thermal analysis results obtained for co-milled ironniobate in Example 2 according to the invention.

FIG. 4 shows the thermal analysis results obtained for co-milled ironniobate in Example 3 according to the invention.

FIG. 5 shows the thermal analysis results obtained for co-milledwolframite-containing ore in Example 4 according to the invention.

FIG. 6 shows the thermal analysis results obtained for co-milledscheelite-containing ore in Example 5 according to the invention.

FIG. 7 shows the thermal analysis results obtained for co-milledgarnierite ore in Example 6 according to the invention.

FIG. 8 shows the thermal analysis results obtained for co-milledzircon-containing ore in Example 7 according to the invention.

FIG. 9 shows the thermal analysis results obtained for a mixturecontaining vanadium-containing magnetite in Comparative Example 2according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In a first aspect, the present invention provides a process forpreparing a complex oxide of at least one metal selected from amongelements of Periodic Table groups 13, 4, 5, 6 and 7, cobalt and nickelwith an alkali metal and/or alkaline earth metal, which processcomprises reacting an oxide of at least one metal selected from thegroup consisting of elements of Periodic Table groups 13, 4, 5, 6 and 7,cobalt and nickel and/or a precursor of the metal oxide, or a substancecontaining the metal oxide and/or precursor thereof, with an alkalimetal salt and/or alkaline earth metal salt. The process ischaracterized by co-milling a mixture of the metal oxide and/or aprecursor thereof, or a mixture of a substance containing the metaloxide and/or a precursor thereof, with an alkali metal salt and/oralkaline earth metal salt to a particle size for the metal oxide and/orprecursor thereof, or for the metal oxide and/or precursor-containingsubstance, of 10 μm or less, and heating the co-milled product to atemperature of at least 200° C. so as to induce a solid-phase reaction.

Preferably, the inventive process for preparing a complex oxide includesthe step to extract the complex oxide of at least one metal selectedfrom among elements of Periodic Table groups 13, 4, 5, 6 and 7, cobaltand nickel with an alkali metal and/or alkaline earth metal from thecomplex oxide-containing reaction product, and thereby recover thecomplex oxide in the aqueous solvent.

In the inventive process for preparing a complex oxide, the metaloxide-containing substance is preferably base ore, refined ore,incinerator ash, industrial waste or non-industrial waste.

In the inventive process for preparing a complex oxide, the precursor ofthe metal oxide is preferably a ferroalloy, alloy, salt or sulfate ofthe metal.

In the inventive process for preparing a complex oxide, the metal in themetal oxide is preferably vanadium, zirconium, niobium, nickel ortungsten.

In the inventive process for preparing a complex oxide, the alkali metalsalt and/or alkaline earth metal salt is preferably a carbonate, ahalide, a sulfate, a borate or a hydroxide.

In the inventive process for preparing a complex oxide, the alkali metalsalt and/or alkaline earth metal salt is preferably sodium carbonate,potassium carbonate, sodium sulfate, calcium carbonate or sodiumhydroxide.

In the inventive process for preparing a complex oxide, the reaction ofthe metal oxide and/or a precursor of the metal oxide, or a substancecontaining the metal oxide and/or precursor thereof, with an alkalimetal salt and/or alkaline earth metal salt is preferably carried out ata temperature of at least 250° C. but below the decomposition point ormelting point, whichever is lower, of the alkali metal salt and/oralkaline earth metal salt.

The invention is described more fully below.

The grinding equipment used in the invention is not subject to anyparticular limitation with regard to type or construction, provided itis capable of grinding the oxide of a value metal and/or a precursorthereof, or a substance containing the metal oxide and/or precursorthereof, to a particle size of 10 μm or less. Illustrative examplesinclude kneaders such as pressurizing kneaders and two-roll mills, aswell as vibratory mills and rotating ball mills. A vibratory mill ispreferred.

The milling conditions vary empirically according to the apparatus used.If a vibratory mill is used, for example, the amplitude of thevibrations will vary by carring out as a batch type or continuousoperation. Also, the amplitude of the vibrations will differ with thepot capacity, although the driving force is generally set to a levelthat provides a frequency somewhat over 10 Hz. Therefore, the feedstock,alkali metal or alkaline earth metal salt, grinding balls and the likeare placed in the pot, the degree of packing by the charge is adjustedaccording to the properties of the feedstock, and the conditions are setso that the co-milling time needed to achieve the target particle sizeis about 30 minutes to 8 hours. Unless milling is carried out to afeedstock particle size having a median of 10 μm or less, and preferably5 μm or less, the surface of the feedstock will have few active sitesand the amount of alkali metal or alkaline earth metal salt that comesinto contact with such active sites will be small. As a result, thesolid-phase reaction between the feedstock and the alkali metal oralkaline earth metal salt at the feedstock surface does not proceed to asufficient degree during co-milling, and a stable interface does notform. When such a co-milled product is then heated, because a stableinterface has not formed, the alkali metal or alkaline earth metal saltdoes not readily penetrate to the interior of the feedstock, in additionto which the distance the salt must move to the feedstock interiorincreases. Hence, this solid-phase reaction fails to proceed to anadequate degree. It is thus critical that co-milling be carried out to afeedstock particle size having a median of 10 μm or less, and preferably5 μm or less.

The median is the particle size which is the center value of themass-based particle size distribution for the feedstock. In the case ofa finely divided powder like the feedstock in the invention, themass-based particle size distribution can be obtained by the laserdiffraction technique. The median can be defined here as the particlesize which is the center value in this particle size distribution.

The value metal oxide of concern in the invention is an oxide of atleast one metal selected from among elements of Periodic Table groups13, 4, 5, 6 and 7, cobalt and nickel and/or a precursor thereof, or asubstance containing the metal oxide and/or the precursor thereof.

Group 13 metals include gallium, indium and thallium, group 4 metalsinclude zirconium, group 5 metals include vanadium, niobium andtantalum, group 6 metals include chromium, molybdenum and tungsten, andgroup 7 metals include technetium and rhenium.

Examples of the value metal oxide-containing substance of concern in theinvention include base ore, refined ore, incinerator ash, industrialwaste and non-industrial waste. Exemplary base ores includevanadium-containing ore, chromium-containing ore, zircon-containing ore,niobium-containing ore, nickel-containing ore and tungsten-containingore. Exemplary refined ores include enriched forms of such minerals inthese base ores as vanadate-containing ore, chrome iron ore, zircon,scheelite, garnierite, magnetite and wolframite. Industrial wastesinclude soot, slag, spent catalyst, scrap, coal ash and wastes such asfrom electronic parts and materials.

Precursors of the above oxides of value metals are compounds which canbe converted into the oxide of a value metal. Such compounds includeferroalloys, alloys, metal salts and sulfates. Exemplary metal saltsinclude carbonates, halides, sulfates, borates, silicates, aluminate andhydroxides. Exemplary alloys include ferrotungsten, ferroniobium,ferrovanadium, ferronickel and ferromolybdenum. For example, to obtain acomplex oxide of niobium, a ferroniobium alloy which is about two-thirdsniobium is preferred.

Examples of the alkali metal salt and/or alkaline earth metal salt whichis reacted with the oxide of a value metal in the invention includecarbonates, halides, sulfates and borates. For the sake of convenience,as used herein, “metal salts” includes also hydroxides and oxides. Ofcourse, mixtures of these can also be used. Some metal salts,particularly alkaline earth metal salts, decompose before they melt.However, if the products of such decomposition are in an active state,they can fully function as the reactant in the invention in the same wayas a melt. Decomposable carbonates and hydroxides are preferred.

The alkali metal is preferably sodium or potassium, and the alkalineearth metal is preferably calcium.

Specific examples of the alkali metal salt and/or alkaline earth metalsalt include carbonates such as sodium carbonate, potassium carbonate,lithium carbonate and calcium carbonate; hydroxides such as sodiumhydroxide and potassium hydroxide; bicarbonates such as sodiumbicarbonate; halides such as sodium chloride and lithium fluoride; andborates such as sodium borate and sodium metaborate. Sodium carbonateand potassium carbonate are especially preferred.

The alkali metal or alkaline earth metal salt is used in at least astoichiometric amount that reacts with the oxide of the value metal toform the complex oxide. The molar ratio varies with the intended complexoxide. For example, to obtain a complex oxide of a specific compositionusing one type of metal salt and one type of value metal oxide, theseare typically mixed in amounts representing the stoichiometric ratio andco-milled, then reacted. Also, to efficiently obtain the desired complexoxide from the compounds in a complex system such as a refined ore andachieve a higher reaction efficiency at the time of extraction andrecovery, it is preferable to use an amount of the alkali metal oralkaline earth metal salt which is 1.2 to 3 times the stoichiometricratio with respect to the value metal oxide included therein.

In the practice of the invention, after co-milling of the feedstock hasbeen completed, the co-milled product is either heated within themilling apparatus or is removed and heated. Heating promotes diffusionof the metal salt or its decomposition products from the solid surfaceinto the solid interior of the co-milled product (i.e., the value metaloxide), and so presumably the solid-phase reaction proceeds not only atthe surface of the value metal oxide but also at the interior therein.

Because heating is carried out to promote diffusion of the alkali oralkaline earth metal salt or its decomposition products from the solidsurface to the solid interior of the co-milled value metal oxide, it ispreferable to promptly carry out such heating after co-milling. Yet,even if the time until the start of heating after co-milling isextended, the completion time for the solid-phase reaction that formsthe complex oxide merely increases by the same amount; from thestandpoint of operational control, all that is required is suitablecontrol of the heating step. In certain cases, however, such as when adeliquescent alkali metal or alkaline earth metal salt is used, ifco-milling is followed by a long interval of time before the start ofheating, the complex oxide may take longer to form. In extreme cases,the solid-phase reaction may even fail to proceed.

Accordingly, it is desirable to carry out process control suitable forthe feedstock and the alkali or alkaline earth metal salt.

The heating method is not subject to any particular limitation. Forexample, one simple and expedient method is to place the co-milledproduct in an ordinary electrical furnace and electrically heat it.Other suitable heating methods include that of passing a hot draftthrough a furnace in which the co-milled product has been loaded, and aradiant heating method that involves externally heating the walls of afurnace in which the co-milled product has been placed.

The heating temperature may be set as appropriate for the type of valuemetal oxide. However, at less than 200° C., diffusion within the solidtakes time, which is undesirable for industrial use. Hence, heating mustbe carried out to at least 200° C., and preferably at least 250° C. Itis essential for the upper limit in the heating temperature to be lessthan the decomposition temperature or the melting temperature, whicheveris lower, of the alkali metal salt and/or alkaline earth metal salt.Heating to a higher temperature than this entails the application ofunnecessary thermal energy, which is economically disadvantageous andmoreover causes the alkali metal salt and/or alkaline earth metal saltto volatize or melt rather than remaining in a solid state, thusinviting such undesirable effects as alkali corrosion of the furnace orthe deposition of reaction products.

If the feedstock contains various impurities, a complex oxide whichincludes the impurities admixed therein will be obtained as the finalproduct.

If the complex oxide obtained by the solid-phase reaction iswater-soluble, in accordance with common practice, the complex oxide canbe separated and recovered by adding, to the solid-phase reactionproduct after heating, an aqueous solvent so as to render the complexoxide into an aqueous solution, then carrying out extraction andfiltering the extract. To increase the extraction concentration andefficiently carry out extraction, it is desirable to take thetemperature dependence of the complex oxide solubility into account andset the extraction temperature so as to obtain a high-concentrationsolution.

If the complex oxide obtained by the solid-phase reaction is insoluble,in accordance with common practice, the complex oxide can be separatedand recovered by dissolving and removing substances other than thecomplex oxide with an acid or an alkali.

The complex oxide that has been recovered is reduced, first to the oxideof the value metal therein, then to the value metal, in accordance withstandard practice.

Examples are given below to illustrate the invention, but should not beconstrued as limitative of the invention. In the examples, theextraction ratio for a complex oxide is calculated as follows.Extraction ratio of complex oxide=[(amount of value metal infiltrate)/(amount of value metal in filtrate+amount of value metal inresidue)]×100

EXAMPLE 1

Vanadium-containing magnetite was electromagnetically separated, givinga refined ore which had a lower level of gangue minerals such as silicaand alumina and the elemental composition, as determined by theinductively-coupled plasma (ICP) method, shown in Table 1 (excludingoxygen; in mass %). After first being coarsely ground to a particle sizeof 0.3 mm or less, this refined ore was ground for 10 minutes in arotating ball mill (model JIS-M=4002, manufactured by Yoshida SeisakushoCo., Ltd.). The powder having a particle size of 300 μm or more obtainedby screening the product was again ground. This grinding operation wasrepeated until none of the powder had a particle size of 300 μm or more,yielding a ground refined ore having a median particle size of 32.3 μm.The median particle size was determined with a laser diffraction-typeparticle size analyzer (HR850B, manufactured by Cilas). This was done byadding 1 g of the ground refined ore and 0.05 g of sodiumhexametaphosphate as a dispersant to 400 ml of ion-exchanged water,carrying out dispersion for 5 minutes in an ultrasonic homogenizer, thenmeasuring the particle size in a quartz cell. TABLE 1 Component Fe Ti VMg Al Si Mn Content 63.2 2.2 1.71 0.09 0.85 0.51 0.13

Four hundred grams of the ground refined ore and 40 g of sodiumcarbonate were co-milled for 90 minutes at an amplitude of 4 mm and anoperating speed of 1200 rpm in a vibratory mill (Vibropot YAMP-6SND,manufactured by Murakami Seiki Mfg. Co., Ltd.) to which had been added280 alumina balls (diameter, 10 mm). The mixture of refined ore andsodium carbonate obtained by co-milling had a particle size, expressedas the median particle size, of 4.3 μm.

Next, 100 g of the co-milled mixture was placed in a muffle furnace andheated for 1 hour in an open-air atmosphere at 600° C. to effect asolid-phase reaction between the oxide of vanadium and the sodiumcarbonate, after which cooling was carried out. Fifty grams of thecooled reaction product and 200 ml of boiling water (pure water) werethen placed in a flask equipped with a condenser and stirred for 45minutes with a stirrer while being heated at 90° C. on a mantle heater,thereby extracting the compl The process for preparing a complex oxideaccording to claim 1, wherein the process includes the step to extractthe complex oxide of at least one metal selected from among elements ofPeriodic ex oxide of vanadium. Following the completion of extraction,the extract was suction filtered while still hot with 5C filter paper.The filtration residue was washed four times with boiling water. Thefiltrate was recovered, placed in a 250 ml graduated flask, and broughtup to 250 ml by adding pure water.

The weight change for 50 mg of the mixture of refined ore and sodiumcarbonate obtained by co-milling was measured with a thermobalance undera 200 ml/min stream of air and at a ramp-up rate of 10 K/min. Theresults are shown as a plot (FIG. 1) of temperature on the x-axis versusthe weight on the y-axis at left and the differential thermocoupleoutput on the y-axis at right. From FIG. 1, it is apparent that thedecrease in weight of the mixture after co-milling ends at about 600° C.and an endotherm appears at the same time. This suggests that a reactionaccompanied by carbon dioxide removal from the sodium carbonate occursup to about 600° C.

The concentrations of vanadium in the filtrate and the residue weremeasured by the ICP method, and the absolute amounts of vanadium in theresidue and the filtrate were computed from these concentrations and theresidue mass and liquid volume (250 ml) to be respectively 35 mg and 696mg. The vanadium extraction ratio was calculated from the above formula,giving a high extraction ratio of 95.2%.

The extraction of vanadium to a high ratio was due to the formation ofsodium metavanadate NaVO₃, which is a water-soluble complex oxide.Presumably, the following solid-phase reaction accompanied by carbondioxide removal took place up to 600° C.V₂O₅+Na₂CO₃→2NaVO₃+CO₂

EXAMPLE 2

A ferroniobium alloy having the elemental composition shown in Table 2(excluding oxygen; in mass %), as determined by the ICP method, wasfirst coarsely ground to a particle size of 0.3 mm or less, then groundusing the vibratory mill described in Example 1 until the portion of thematerial having an average particle size of 200 mesh (75 μm) or lessaccounted for 50 wt % of the overall material, thereby giving a groundferroniobium alloy having a median particle size of 71.0 μm.

The mass change for 50 mg of the ground ferroniobium alloy was measuredwith a thermobalance under a 200 ml/min stream of air and at a ramp-uprate of 10 K/min. The results are shown as a plot (FIG. 2) oftemperature on the x-axis versus the mass on the y-axis at left and thedifferential thermocouple output on the y-axis at right. From FIG. 2, itis apparent that the rise in weight of the ferroniobium alloy stops andoxidation ends at about 900° C. TABLE 2 Component Nb Fe Si Al Ta P SContent 66.3 29.8 0.15 1.12 0.02 0.07 0.08

Next, 300 g of the ground ferroniobium alloy was placed in a mufflefurnace, heated for 1 hour at 950° C. under a stream of air, thencooled. The cooled product was subjected to x-ray diffraction analysis,confirming that the ferroniobium alloy had converted into iron niobateFeNbO₄.

Four hundred grams of the cooled iron niobate-containing mixture and 40g of sodium carbonate were co-milled for 90 minutes at an amplitude of 4mm and an operating speed of 1200 rpm in the above-described vibratorymill to which had been added 280 alumina balls (diameter, 19 mm). Themixture of the iron niobate-containing mixture and sodium carbonateobtained by co-milling had a particle size, expressed as the medianparticle size, of 3.3 μm.

The mass change for 50 mg of the mixture of the iron niobate-containingmixture and sodium carbonate obtained by co-milling was measured with athermobalance under a 200 ml/min stream of air and at a ramp-up rate of10 K/min. The results are shown as a plot (FIG. 3) of temperature on thex-axis versus the mass on the y-axis at left and the differentialthermocouple output on the y-axis at right. From FIG. 3, it is apparentthat the decrease in mass of the mixture starts at about 400° C. andends at 780° C., and that an endotherm appears at the same time at 780°C.

Next, 100 g of the co-milled mixture of the iron niobate-containingmixture and sodium carbonate was placed in a muffle furnace and heatedfor 1 hour in an open-air atmosphere at 800° C. to effect a solid-phasereaction between the oxide of niobium and the sodium carbonate, afterwhich cooling was carried out. After cooling, the solid-phase reactionproduct was subjected to x-ray diffraction analysis, from which it wasconfirmed to contain the complex oxide sodium metaniobate NaNbO₃. Thesodium metaniobate was extracted with water to an extraction ratio of94.7%.

From the above, the following solid-phase reaction is presumed to havetaken place, forming sodium metaniobate.2FeNbO₄+Na₂CO₃→2NaNbO₃+Fe₂O₃+CO₂

EXAMPLE 3

Two hundred grams of the cooled iron niobate-containing mixture fromExample 2 and 200 g of sodium carbonate were co-milled for 120 minutesat an amplitude of 4 mm and an operating speed of 1200 rpm in thevibratory mill described in Example 1 to which had been added 280alumina balls (diameter, 19 mm). The mixture of the ironniobate-containing mixture and sodium carbonate obtained by co-millinghad a particle size, expressed as the median particle size, of 2.5 μm.

The mass change for 50 mg of the mixture of the iron niobate-containingmixture and sodium carbonate obtained by co-milling was measured with athermobalance under a 200 ml/min stream of air and at a ramp-up rate of10 K/min. The results are shown as a plot (FIG. 4) of temperature on thex-axis versus the mass on the y-axis at left and the differentialthermocouple output on the y-axis at right. From FIG. 4, it is apparentthat the mass loss by the mixture starts at about 400° C. and ends at800° C., and that an exotherm appears at the same time at 800° C. Inaddition, the exotherm is accompanied by an endotherm. In Example 2, ascan be seen in FIG. 3, there is only an exotherm. Hence, in Example 3,some sort of phase change apparently occurs.

Next, 100 g of the co-milled mixture containing the ironniobate-containing mixture and sodium carbonate was placed in a mufflefurnace and heated for 1.5 hours in an open-air atmosphere at 800° C. soas to effect a solid-phase reaction between this iron niobate FeNbO₄ andthe sodium carbonate, after which cooling was carried out. Aftercooling, the solid-phase reaction product was subjected to x-raydiffraction analysis, from which the formation of sodium orthoniobateNa₃NbO₄, which is a complex oxide of niobium, was confirmed. Two gramsof the cooled solid-phase reaction product and 200 ml of boiling water(pure water) were placed in a flask equipped with a condenser andstirred with a stirrer for 60 minutes while being heated at 90° C. on amantle heater, thereby carrying out extraction of the sodiumorthoniobate. Following completion of the extraction, the extract wassuction filtered with 5C filter paper. The filtration residue was washedfour times with boiling water. The filtrate was recovered, placed in a250 ml graduated flask, and brought up to 250 ml by adding pure water.

The concentrations of niobium in the filtrate and the residue weremeasured by the ICP method, and the absolute amounts of niobium in theresidue and the filtrate were computed from these concentrations and theresidue mass and volume (250 ml) to be respectively 0.06 g and 5.38 g.The niobium extraction ratio was calculated, yielding a high extractionratio of 98.9%.

From the above, the following solid-phase reaction presumably tookplace, resulting in the formation of sodium orthoniobate.2FeNbO₄+3Na₂CO₃→2Na₃NbO₄+Fe₂O₃+3CO₂

EXAMPLE 4

A wolframite-containing base ore having the elemental composition shownin Table 3 (excluding oxygen; in mass %), as determined by the ICPmethod, was coarsely ground to a particle size of 0.3 mm or less, thenground using the rotating ball mill described in Example 1 until theportion of the material having an average particle size of 400 mesh (36μm) or less accounted for 80 mass % of the overall material, therebygiving a ground wolframite-containing ore having a median particle sizeof 52.3 μm.

Two hundred grams of the divided wolframite-containing ore and 95 g ofpotassium carbonate were co-milled therein for 90 minutes at anamplitude of 4 mm and an operating speed of 1200 rpm in theabove-described vibratory mill to which had been added 260 iron balls(diameter, 19 mm). The ore and potassium carbonate-containing mixtureobtained by co-milling had a particle size, expressed as the medianparticle size, of 3.9 μm.

The mass change for 50 mg of the mixture of ore and potassium carbonateobtained by co-milling was measured with a thermobalance under a 200ml/min stream of air and at a ramp-up rate of 10 K/min. The results areshown as a plot (FIG. 5) of temperature on the x-axis versus the mass onthe y-axis at left and the differential thermocouple output on they-axis at right. The loss of mass associated with the sharp endotherm upto 100° C. is due to the evaporation of water vapor absorbed by thepotassium carbonate. The loss of mass that occurs after 300° C. is dueto the release of carbon dioxide from the potassium carbonate. Potassiumcarbonate melts at 800° C., and decomposes at temperatures above this.The mass changes in this mixture indicate that a solid-phase reactionaccompanied by the removal of carbon dioxide proceeds from asurprisingly low temperature.

Next, 100 g of the co-milled ore and potassium carbonate-containingmixture was placed in a muffle furnace and heated for 2 hours in anopen-air atmosphere at 400° C., then cooled. A portion of the cooledmixture was subjected to x-ray diffraction analysis, whereupon thedisappearance of (Fe, Mn)WO₄ and the formation of the complex oxidepotassium tungstate K₂WO₄ were noted. When this data is consideredtogether with the results of thermal analysis, it appears that thefollowing solid-phase reaction proceeded to completion by 400° C.(Fe,Mn)WO₄+K₂CO₃→(Fe,Mn)O+K₂WO₄+CO₂

Fifty grams of the cooled mixture containing ore and potassium carbonateand 200 ml of boiling water (pure water) were placed in a flask equippedwith a condenser and stirred with a stirrer for 30 minutes while beingheated at 90° C. on a mantle heater, thereby carrying out extraction ofthe complex oxide of tungsten. Following the completion of extraction,the extract was suction filtered with 5C filter paper. The filtrationresidue was washed four times with boiling water. The filtrate wasrecovered, placed in a 250 ml graduated flask, and brought up to 250 mlby adding pure water.

The concentrations of tungsten in the filtrate and the residue weremeasured by the ICP method, and the absolute amounts of the complexoxide of tungsten in the residue and the filtrate were computed fromthese concentrations and the residue mass and volume (250 ml) to berespectively 0.4 g and 15.1 g. The niobium extraction ratio wascalculated, yielding a high extraction ratio of 97.4%.

In addition to the results of thermal analysis and x-ray diffractionanalysis, given that the tungsten was extracted with an aqueoussolution, the above solid-phase reaction presumably took place,resulting in the formation of potassium tungstate.

EXAMPLE 5

A scheelite-containing base ore having the elemental composition shownin Table 4 (excluding oxygen; in mass %), as determined by the ICPmethod, was coarsely milled to a particle size of 0.3 mm or less, thenground using the rotating ball mill described in Example 1 until theportion of the material having an average particle size of 400 mesh (36μm) or less accounted for 80 mass % of the overall material, therebygiving a milled scheelite-containing ore having a median particle sizeof 49.0 μm. TABLE 4 Component W Si Ca Al Fe Mg Na S Content 18.3 19.99.11 3.60 3.68 0.69 1.09 0.67

Two hundred fifty grams of the ground scheelite-containing ore and 80 gof sodium carbonate were co-milled therein for 1 hour at an amplitude of4 mm and an operating speed of 1200 rpm in the vibratory mill describedin Example 1 to which had been added 260 iron balls (diameter, 19 mm).The mixture of scheelite-containing ore and sodium carbonate obtained byco-milling had a particle size, expressed as the median particle size,of 3.1 μm.

The mass change for 20 mg of the mixture of ore and sodiumcarbonate-containing mixture obtained by co-milling was measured with athermobalance under a 200 ml/min stream of air and at a ramp-up rate of2 K/min. The results are shown as a plot (FIG. 6) of temperature on thex-axis versus the mass on the y-axis at left and the differentialthermocouple output on the y-axis at right.

The loss of mass that occurs after 400° C. is due to the release ofcarbon dioxide from the sodium carbonate. Sodium carbonate melts at 850°C., and decomposes at temperatures above this. The mass changes in thismixture indicate that a solid-phase reaction accompanied by the removalof carbon dioxide from the sodium carbonate proceeds from a surprisinglylow temperature.

Next, 100 g of the ore and sodium carbonate-containing mixture obtainedby co-milling was placed in a muffle furnace and heated for 1.5 hours inan open-air atmosphere at 600° C., then cooled. A portion of the cooledmixture was subjected to x-ray diffraction analysis, whereupon thedisappearance of CaWO₄ and the formation of the complex oxide sodiumtungstate Na₂WO₄ were noted. When this data is considered together withthe results of thermal analysis, it appears that the followingsolid-phase reaction proceeded to completion by 600° C.CaWO₄+Na₂CO₃→CaO+Na₂WO₄+CO₂

Fifty grams of the cooled mixture containing ore and sodium carbonateand 200 ml of boiling water (pure water) were placed in a flask equippedwith a condenser and stirred with a stirrer for 30 minutes at ambienttemperature, thereby carrying out extraction of the complex oxide oftungsten. Following completion of the extraction, the extract wassuction filtered with 5C filter paper. The filtration residue was washedfour times with boiling water. The filtrate was recovered, placed in a250 ml graduated flask, and brought up to 250 ml by adding pure water.

The concentrations of tungsten in the filtrate and the residue weremeasured by the ICP method, and the absolute amounts of tungsten in theresidue and the filtrate were computed from these concentrations and theresidue mass and volume (250 ml) to be respectively 0.13 g and 7.83 g.The tungsten extraction ratio was calculated, yielding a high extractionratio of 98.4%.

EXAMPLE 6

A garnierite-containing base ore having the elemental composition shownin FIG. 5 (excluding oxygen; in mass %), as determined by the ICPmethod, was coarsely ground to a particle size of 0.3 mm or less, thenground using the rotating ball mill described in Example 1 until theportion of the material having an average particle size of 400 mesh (36μm) or less accounted for 90 mass % of the overall material, therebygiving a ground garnierite-containing ore having a median particle sizeof 38.1 μm.

In addition, using a thermal analysis system with mass spectrometer(Thermo Mass, manufactured by Rigaku Corporation), 2 mg of the milledgarnierite ore was heated at a ramp-up rate of 10 K/min to examine themass loss behavior, in addition to which the emitted gas was analyzed.Given that the emission of gas substantially ended at 700° C. and thegas was composed entirely of water, it is assumed that a dehydrationreaction involving conversion of the hydroxide to an oxide proceeded.TABLE 5 Component Ni Si Ca Al Mg Cr Fe Content 4.84 29.6 <0.1 <0.1 10.70.23 3.72

Next, 300 g of the ground garnierite ore was placed in a muffle furnaceand subjected to dehydration by heating for 2 hours in an open-airatmosphere at 700° C., then cooled. Two hundred grams of the dehydratedgarnierite ore and 80 g of sodium sulfate were co-milled therein for 2hours at an amplitude of 4 mm and an operating speed of 1200 rpm in thevibratory mill described in Example 1 to which had been added 260 ironballs (diameter, 19 mm). The mixture of garnierite ore and sodiumsulfate obtained by co-milling had a particle size, expressed as themedian particle size, of 2.1 μm.

The mass change for 30 mg of the mixture of garnierite ore and sodiumsulfate obtained by co-milling was measured with a thermobalance under a200 ml/min stream of air and at a ramp-up rate of 10 K/min. The resultsare shown as a plot (FIG. 7) of temperature on the x-axis versus theweight on the y-axis at left and the differential thermocouple output onthe y-axis at right.

The loss of mass that occurs after 520° C. is due to the release ofsulfur dioxide from the sodium sulfate. Sulfur dioxide release ends at660° C. Sodium sulfate melts at 880° C., and decomposes at temperaturesabove this. The mass changes in this mixture indicate that a solid-phasereaction accompanied by the removal of sulfur dioxide from the sodiumsulfate proceeds from a temperature at least 200° C. lower than thedecomposition temperature for sodium sulfate by itself.

Hence, 100 g of the garnierite ore and sodium sulfate-containing mixtureobtained by co-milling was placed in a muffle furnace and heated for 1hour in an open-air atmosphere at 700° C., then cooled. A portion of thecooled mixture was subjected to x-ray diffraction analysis, whereuponformation of the complex oxide NaNiO₂ was noted. When this data isconsidered together with the results of thermal analysis, it appearsthat the following solid-phase reaction proceeded to completion by 700°C.2NiO+Na₂SO₄→2NaNiO₂+SO₂

Fifty grams of the cooled mixture containing garnierite ore and sodiumsulfate and 200 ml of 0.1N sulfuric acid in water were placed in a flaskequipped with a condenser and stirred with a stirrer for 30 minutes atambient temperature, thereby carrying out extraction of the complexoxide of nickel. Following completion of the extraction, the extract wassuction filtered with 5C filter paper. The filtration residue was washedfour times with 0.1N sulfuric acid. The filtrate was recovered, placedin a 250 ml graduated flask, and brought up to 250 ml by adding purewater.

The concentrations of nickel in the filtrate and the residue weremeasured by the ICP method, and the absolute amounts of nickel in theresidue and the filtrate were computed from these concentrations and theresidue weight and volume (250 ml) to be respectively 0.16 g and 1.95 g.The nickel extraction ratio was calculated, yielding a high extractionratio of 92.4%.

EXAMPLE 7

One hundred fifty grams of a zircon-containing base ore (100 mass % ofwhich had a particle size of 250 μm or less; 30 mass % of which had aparticle size of 100 μm or less; median particle size, 98.2 μm) havingthe elemental composition shown in Table 6 (excluding oxygen; in mass%), as determined by the ICP method, and 203 g of calcium carbonate wereco-milled for 2.5 hours at an amplitude of 4 mm and an operating speedof 1200 rpm in the vibratory mill described in Example 1 to which hadbeen added 260 iron balls (diameter, 19 mm). The mixture ofzircon-containing ore and calcium carbonate obtained by co-milling had aparticle size, expressed as the median particle size, of 6.0 μm.

The mass change for 50 mg of the mixture of zircon-containing ore andcalcium carbonate obtained by co-milling was measured with athermobalance under a 200 ml/min stream of air and at a ramp-up rate of10 K/min. The results are shown as a plot (FIG. 8) of temperature on thex-axis versus the mass on the y-axis at left and the differentialthermocouple output on the y-axis at right.

The loss of mass that occurs after 500° C. is due to the release ofcarbon dioxide from the calcium carbonate. Such release is completed at730° C. Calcium carbonate decomposes at 825° C. The mass changes in thismixture indicate that a solid-phase reaction accompanied by the removalof carbon dioxide from the calcium carbonate proceeds from a temperatureat least 190° C. lower than the decomposition temperature for calciumcarbonate by itself. TABLE 6 Component Zr Si Fe Ti Al Ca Content 49.415.3 0.05 0.09 0.23 0.02

Next, 100 g of the mixture of zircon-containing ore and calciumcarbonate obtained by co-milling was placed in a muffle furnace andheated for 2 hours in an open-air atmosphere at 750° C., then cooled. Aportion of the cooled mixture was subjected to x-ray diffractionanalysis, whereupon peaks were noted for the complex oxide calciumzirconate CaZrO₃ and for calcium metasilicate CaSiO₃. When this data isconsidered together with the results of thermal analysis, it appearsthat the following solid-phase reaction proceeded to completion by 750°C.ZrSiO₄+2CaCO₃→CaZrO₃+CaSiO₃+2CO₂

Fifty grams of cooled product from the reaction of the zircon-containingore with the calcium carbonate and 200 ml of 0.1N hydrochloric acid inwater were placed in a flask and stirred with a stirrer for 30 minutesat ambient temperature, thereby dissolving and removing the calciummetasilicate and other substances. The solid thus obtained was washedfour times with 0.1N hydrochloric acid, then was washed four times withpure water. A portion of this solid was subjected to x-ray diffractionanalysis, from which the formation of calcium zirconate was confirmed.

Comparative Example 1

The mixture of refined ore and sodium carbonate having a median particlesize of 4.3 μm obtained by co-milling the refined ore and sodiumcarbonate in Example 1 was subjected, without heating, to extractiontreatment with hot water. The extraction ratio was 0.24 wt %, which isvery low. The surface of the extract was presumably sodium metavanadateNaVO₃, which is a complex oxide.

Comparative Example 2

The refined ore having a median particle size of 32.3 μm in Example 1was additionally milled using the vibratory mill described in Example 1,thereby yielding a ground product having a median particle size of 4.0μm.

Next, 200 ml of water was added to 400 g of the ground refined ore and40 g of sodium carbonate and kneading was carried out, following whichthe kneaded material was dried at 120° C. for 8 hours.

The mass change for 50 mg of the kneaded product after drying wasmeasured with a thermobalance under a 200 ml/min stream of air and at aramp-up rate of 10 K/min. The results are shown as a plot (FIG. 9) oftemperature on the x-axis versus the mass on the y-axis at left and thedifferential thermocouple output on the y-axis at right. From FIG. 9, itis apparent that the weight loss in the kneaded product began at 600° C.and ended at 840° C. At the same time, an endotherm appears at 839° C.

Next, 100 g of the kneaded product after drying was placed in a mufflefurnace and heated for 1 hour in an open-air atmosphere at 600° C., thencooled. Fifty grams of the kneaded product after cooling and 200 ml ofboiling water (pure water) were placed in a flask equipped with acondenser and stirred with a stirrer for 45 minutes while heating at 90°C. on a mantle heater, thereby carrying out extraction. Following thecompletion of extraction, the extract was suction filtered with 5Cfilter paper while still hot. The filtration residue was washed fourtimes with boiling water. The filtrate was recovered, placed in a 250 mlgraduated flask, and brought up to 250 ml by adding pure water. Theextraction rate was 3.8%, which was low.

INDUSTRIAL APPLICABILITY

The present invention is able to speed up the rate of the value metalcomplex oxide forming reaction from a metal oxide and/or a precursorthereof, or a substance containing the metal oxide or its precursor,increase the conversion ratio, and provide a high selectivity withoutcausing the eutectic-forming alkali metal or alkaline earth metal saltto melt, that is, without heating to an excessively high temperature.The result is excellent productivity for complex oxides of value metals.Moreover, regardless of the content of the oxides of value metals, theinventive process can efficiently isolate and recover such oxides fromvarious kinds of base ore, industrial wastes and non-industrial wastes,and should prove highly beneficial for industrial scale production.

1. In a process for preparing a complex oxide of at least one metalselected from among elements of Periodic Table groups 13, 4, 5, 6 and 7,cobalt and nickel with an alkali metal and/or alkaline earth metal,which the process comprises reacting an oxide of at least one metalselected from the group consisting of elements of Periodic Table groups13, 4, 5, 6 and 7, cobalt and nickel and/or a precursor of the metaloxide, or a substance containing the metal oxide and/or precursorthereof, with an alkali metal salt and/or alkaline earth metal salt, theprocess is characterized by co-milling a mixture of the metal oxideand/or a precursor thereof, or a mixture of a substance containing themetal oxide and/or a precursor thereof, with an alkali metal salt and/oralkaline earth metal salt to a particle size for the metal oxide and/orprecursor thereof, or for the metal oxide and/or precursor-containingsubstance, of 10 μm or less, and heating the co-milled product to atemperature of at least 200° C. so as to induce a solid-phase reaction.2. The process for preparing a complex oxide according to claim 1,wherein the process includes the step to extract the complex oxide of atleast one metal selected from among elements of Periodic Table groups13, 4, 5, 6 and 7, cobalt and nickel with an alkali metal and/oralkaline earth metal from the complex oxide-containing reaction productby using an aqueous solvent, and thereby recover the complex oxide inthe aqueous solvent.
 3. The process for preparing a complex oxideaccording to claim 1, wherein the metal oxide-containing substance isbase ore, refined ore, incinerator ash, industrial waste ornon-industrial waste.
 4. The process for preparing a complex oxideaccording to claim 1, wherein the precursor of the metal oxide is aferroalloy, alloy, salt or sulfate of the metal.
 5. The process forpreparing a complex oxide according to claim 1, wherein the metal in themetal oxide is vanadium, zirconium, niobium, nickel or tungsten.
 6. Theprocess for preparing a complex oxide according to claim 1, wherein thealkali metal salt and/or alkaline earth metal salt is a carbonate, ahalide, a sulfate, a borate or a hydroxide.
 7. The process for preparinga complex oxide according to claim 6, wherein the alkali metal saltand/or alkaline earth metal salt is sodium carbonate, potassiumcarbonate, sodium sulfate, calcium carbonate or sodium hydroxide.
 8. Theprocess for preparing a complex oxide according to claim 1, wherein thereaction of the metal oxide and/or a precursor of the metal oxide, or asubstance containing the metal oxide and/or precursor thereof, with analkali metal salt and/or alkaline earth metal salt is carried out at atemperature of at least 250° C. but below the decomposition point ormelting point, whichever is lower, of the alkali metal salt and/oralkaline earth metal salt.
 9. In a process for preparing a complex oxideof at least one metal selected from among elements of Periodic Tablegroups 13, 4, 5, 6 and 7, cobalt and nickel with an alkali metal and/oralkaline earth metal, which the process comprises reacting an oxide ofat least one metal selected from the group consisting of elements ofPeriodic Table groups 13, 4, 5, 6 and 7, cobalt and nickel and/or aprecursor of the metal oxide, or a substance containing the metal oxideand/or precursor thereof, with an alkali metal salt and/or alkalineearth metal salt, the process is characterized by co-milling a mixtureof the metal oxide and/or a precursor thereof, or a mixture of asubstance containing the metal oxide and/or a precursor thereof, with analkali metal salt and/or alkaline earth metal salt to a particle sizefor the metal oxide and/or precursor thereof, or for the metal oxideand/or precursor-containing substance, of 10 μm or less, and heating theco-milled product to a temperature of at least 250° C. but below thedecomposition point or melting point, whichever is lower, of the basicsalt so as to induce a reaction.
 10. The process for preparing a complexoxide according to claim 2, wherein the metal oxide-containing substanceis base ore, refined ore, incinerator ash, industrial waste ornon-industrial waste.
 11. The process for preparing a complex oxideaccording to claim 2, wherein the precursor of the metal oxide is aferroalloy, alloy, salt or sulfate of the metal.
 12. The process forpreparing a complex oxide according to claim 2, wherein the metal in themetal oxide is vanadium, zirconium, niobium, nickel or tungsten.
 13. Theprocess for preparing a complex oxide according to claim 2, wherein thealkali metal salt and/or alkaline earth metal salt is a carbonate, ahalide, a sulfate, a borate or a hydroxide.
 14. The process forpreparing a complex oxide according to claim 2, wherein the reaction ofthe metal oxide and/or a precursor of the metal oxide, or a substancecontaining the metal oxide and/or precursor thereof, with an alkalimetal salt and/or alkaline earth metal salt is carried out at atemperature of at least 250° C. but below the decomposition point ormelting point, whichever is lower, of the alkali metal salt and/oralkaline earth metal salt.